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Genera of /ty-WonMs. The difpofition of the ftigmata, or air-holes, at which the tracheae of thefe animals terminate, will help us to the occafions of feveral distinctions of genera among the fly-Worms of variable heads. The Worm of the common flefh-fly has in its fligmata fix aper- tures, three in each, of an oblong figure, and refembling but- ton-holes j but, inftead of thefe, the Worms of many other flies have them in the fame part of their bodies, but have, inftead of the three button-holes, only one fmall eminence, refembling a little button in each : Others have them cylin- dric and hollow, and (landing out from the hinder part of their bodies in form of horns. Some genera have only two of thefe horns, and others have three : The two in fome are placed to a confiderable diftance from one another, and in others they are in a manner joined together. Some alfo carry thefe pipes or horns in an elevated pofition, others having them placed flat on their bodies ; and befide thefe varieties in the number, form, and fituations of the ftigmata, fome distinctions of genera may be drawn from the parts which furround them, and are deftined by nature for their defence. The number, difpofition, and figure of the hooks, which {ervc thefe creatures in the place of teeth, may alfo ferve for matter of distinction, as may alfo the differences of their legs. Reaumur, Hilt. Inf. vol. 4. p. 173. The common Worm of the flefh fly has two hooks, placed at a diftance, in a parallel direction, and a dart between them. Others have thefe hooks, but have no dart ; others have thefe hooks of very different fize one from the other, and placed one over the other ; others have only one fingle hook ; and 6thers there are, which have nothing of this kind at all, or, at leaft, which we can never make to {hew any. Ibid. The figure of the body in others, will alfo give matter ofdi- ftinction. The hinder part of fome is, as it were, cut off, and reprefents the truncated end of a cylinder. Some there are of a much fhorter body than others ; fome have their ante- rior part as thick as the posterior : fome are more flat, and others more round. Ibid. p. 174.
Notwithstanding that thefly-Worms of the firft clafs have, pro- perly fpeaking, no legs, yet feveral of them are able, at plea- sure, to inflate themfelves, and to fend out from the under part of the rings of their body, in that ftate, certain membra- naceous portions analogous to, and fupplying the place of legs, and much variety is to be obferved in the placing of thefe. Some have them arranged orderly as legs, two and two, one on each fide of each ring ; others have a fingle range of them all along their belly, in a row down the middle. Each of thefe is fometimes furcated or divided into two; and others have the under part of their bodies, at or near the junction of the
■ rings, furniihed with a fort of hooks, very fhort and fine, and commonly of a red colour ; thefe are of great ufe to the creature in laying hold of the furface on which it moves it- felf. Ibid.
The differences of fize and colour In thefe creatures, may alfo be made the bafis of farther distinctions ; among other things, the nature and quality of the flans of the different kinds may alfo be confidered, fome being thin and tranfparcnt, others thick, rigid, and opake ; fome alfo being fmooth, others rough and wrinkled, others adorned with long hairs, and finally' others, as it were, armed with prickles. Thefe are the marks and characters of the genera of the firft clafs. Thefe of the fecond, which have variable heads, and differ from the former in that they have legs like thofe of the caterpillar- clafs, have frequently a fort of thorns or hooks fattened to them, and though the head of the Worms of this clafs is truly of a variable figure, and is flefhy, the mouth is ever fo vifible in all its changes, that the head is eafily known to befuch.
Another very obvious character there alfo is of the generality of the Worms of this clafs, which is, that they have a long flefhy tail, which they can lengthen or fhorten as their occa- fions require ; the refemblance of this to the tail of a rat may probably give this genus the name of the rat-tailed Worms. This tail is the principal organ of refpiration in thefe Worms ; its end is always open, and fupplies the office of the ftigmata of the other genera. Ibid.
The fly-Worms of the third clafs, which have their heads of a conftant and invariable figure, and, like thofe of other animals, have no moveable jaws, or any thing analogous to that orga- nization ; but fuch of them as have any teeth or hooks, have all a power of drawing them into their heads on occafion, and only throw them out when they would ufe them. The Worms of this clafs have pointed heads, or fuch as feem truncated, or with the end of the rays part cut off, they have no fhelly or fcaly legs. Thefe are a very numerous family both in the terreftrial and aquatic kingdom, and all, as far as is hitherto known, furnifh two-winged flies. The firft genus of thefe may be eftablifhed of the fcaly fpecies, which have, as it were, Scaly rings, and are rigid, and not incapable of flexion, though wholly fo of contraction or dila- tation ; thefe Worms can turn about nimbly enough, but can- not at all lengthen or fhorten their bodies, and thence may be properly enough called the ferpeniine genus. The former genus are naturally inhabitants of the earth j thofe •f the waters give us a fecund genus. Thefe have a merely
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membranaceous fkin, and always an oblong head, and their pofterior extremity is terminated by a fort of pipe, open at the end for refpiration. Tie bodies of thefe are round, or approaching to that figure. Ibid. p. 178. Another genus may well be efhuiifhed of the Worms with heads like the former, but with flatter bodies. There are two fpecies of this frequently found, the one in cow-dung, the other in the agarics of the fycamore, and other trees. Thefe have their organs of refpiration, like the reft, in the hinder part of their bodies, and they might in many be miftaken for the arms of the creature, by thofe not converfant among the crea- tures of this clafs.
A, fourth genus may be eftablifhed of the Worms of long and rounded bodies, which are fmaller at each end than in the middle ; thefe may be called the tipula-Wonns, becaufe they all are transformed into flics of that clafs. The head of thefe Worms is fcaly, and fmall in proportion to the fize of their body, and their ftigmata are placed in the hinder part of their bodies, and furrounded with a flefhy appendix. Ibid. p. 179. T here is another genus of Worms which transform themfelves into tipuke, and perhaps merit a feparate clafs, rather than a fubordinate genus. Thefe are altogether red, and of a bright lively colour : they have near their head two Short legs, which refemble two flumps of arms ; but the thing that, above all others, characterifes thefe, is, that they have, near their hin- der extremity, and on the under part of their bodies, four long flefhy firings, which having fome refemblance to the po-- lype-fifh, may well enough give thefe the name of the po- lype-Worm. Thefe have alfo, at the hinder part of their bo- dies, two cylincric pipes, which have much of the appearance of organs of refpiration. Ibid. p. 180.
A fixth genus may alfo be eftablifhed of the water-Worms, which are transformed into gnats. Thefe refpirc like the reft, by means of the hinder extremity of their body, which is an open pipe ; they have alfo, befide this, another pipe, deftined to give pafTage to the excrements, and placed under their body. Ibid.
A feventh genus may be eftablifhed of thofe long Worms, re- fembling the Worms of the tipulze, and having a fmall fcaly head : Thefe live in the earth, and in cow-dung, and are co- vered with hairs, which give them much the appearance of caterpillars. Thefe have two ftigmata placed in their hinder part, furrounded with flefhy appendages.
An eighth genus may be eftablifhed of the long, white, and ftiining, but not fcaly Worms, frequently found in and among mufhrooms. Thefe have their ftigmata not placed behind, as the reft of the fly-Worms have ; but, like thofe of the cater- pillars, in every ring of their body.
The Worms of the fifth clafs, which ufually produce four- winged flies, have heads of a conftant and invariable figure, and have two teeth, or two moveable jaws, always open and expofed, and which are placed near the middle of the aperture of the mouth; they have no fcaly legs. Ibid. The ftigmata of thefe Worms are placed on their fides, and never on the hinder parts of their bodies. The flies produced from thefe are of very numerous genera, the bees, wafps, ichneumons, gall-flies, &c. are all of this fort. Ibid. p. 182. The fixth clafs of thefe Worms is that of the hexapode, or fix- legged kind, which are transformed into fome fpecies of the libelee. Thefe have no mouth, but inftead of one, have, in a manner, two, if the openings through which their aliments pafs, may be fo called. Thefe are at the top of their antenna;, which are placed in the fore-part of their head. The fly- Worms of this fingular clafs, are but very few in num- ber. The formica- leo, in the ftate in which it is known by that name, is one, and the puceron-eaters are fo many others. Ibid. p. 183.
The feventh clafs is of the Worms which have bodies lonn- like the caterpillar- clafs, and have fix legs; but their fingular character is, that they have two other fhort legs, or properly two hooks of a particular kind, placed near their hinder part, and aflifting them infixing themfelves, and moving. The wa- tcr-Worms, which make themfelves cafes of different mate- rials, and are afterwards transformed into papilionaceous flies, are of this clafs.
Several fmall green and yellow Worms, which feed on the apri- cock and pear-tree, and fold up the leaves of thofe trees, tho* they much rcfemble caterpillars, are alfo truly and properly of this clafs.
The eighth clafs is of thofe Worms called falfe or hajlard cater- pillars, becaufe the figure of their body might make them be miftaken for caterpillars, rather than known for Ay- Worms, by lefs curious obfervers.
Thefe have fix cruftaceous legs, like the caterpillars ; but they have a greater number of the membranaceous ones than thofe infects ; they have fcarce ever lefs than ten, and often four- teen. Thefe alfo are not edged round with hooks, as thofe of the caterpillars are ; and they differ from the true caterpillars in this alfo, that their head is more round, and has only two eyes, one on each fide ; whereas the caterpillars have on each fide five or fix, difpofed in form of an arch. Ibid. p. 185. All this clafs of Worms, fo far as is yet known, change into four-winged flies ; the females of which are armed with- a faw behind. The number of the membranaceous legs being dif- 1 tefent
